This invention relates to a device for controlling a cycloid propeller for watercraft.
In order to precisely maneuver ferry boats, floating cranes, passenger liners, buoy boats, trawlers or other watercrafts within a minimum amount of space or to keep such watercrafts exactly in one and the same spot, such crafts are preferably equipped with a plurality of cycloid propellers, generally referred to as "Voith-Schneider propellers". These prior art cycloid propellers are propeller wheels which protrude from the bottom of the craft and rotate about a generally vertical axis. A plurality of blades are arranged on the circumference of these propeller wheels and these blades pivot individually about axes which are also generally vertical. German Patent No. 2 029 995 discloses a control for these blades. The principle of operation of such prior art propeller wheels is shown in FIG. 1, of the instant application.
Referring to FIG. 1, three to seven pivoting blades 2 through 6 are arranged on the propeller wheel 1. These blades are pivoted relative to the wheel tangent through an angle which is varied over a complete revolution of the propeller wheel between a maximum positive and a maximum negative angular value (the so-called "pitch"). The propeller wheel is arranged on the bottom of the watercraft, hereinafter referred to as a ship, in such a way that its axis of rotation is substantially vertical whereby the water exerts forces K2-K6 on the pivoting blades. The vector addition of these forces produces a resultant force which increases with an increase in the angle of the pivoting blades relative to the wheel tangent.
With F marking the longitudinal axis of the ship and with points 7, 7' marking the intersections of this axis with the circle 1, the angle f of the pivoting blades at points 7, 7' (called "travel pitch") produces the thrust which moves the ship in the direction of the longitudinal axis F, which is the normal direction of travel of the ship.
If the position of the pivoting blades at points 8 and 9 is varied from the position shown in FIG. 1, so that a "rudder pitch" is imparted to the blades, as measured by the angular position of the pivoting blades relative to the wheel tangent at points 8 and 9, a thrust force component in the direction of the "rudder axis" R will be generated.
To adjust the position of the pivoting blades, an adjustable so-called "control point" A is provided in the propeller wheel transmission. The eccentricities of control point A relative to the propeller wheel, as measured by Cartesian components DF, DR in the coordinate system F, R, determine the pitch of the blades as the propeller wheel revolves.
The thrust forces occurring in the directions F and R which are produced by the propeller wheel and its drive depend on the flow of water which impinges on the propeller wheel. More specifically, the thrust forces are dependant on the geometry of the ship bottom and the relative speed of travel of the ship. These variables can be allowed for by the control characteristics of the propeller wheel. With respect to the loading of the drive and the limitation of the eccentricities, it has been shown to be advantageous to reduce the travel pitch as a function of the rudder pitch, as shown by characteristic 10 in FIG. 1. The control axis A of the propeller wheel transmission is adjusted with the aid of two electrically controlled actuators 11 and 12 and a driving mechanism (not illustrated). If these actuators are located in the axes F and R, the adjustment paths DX and DY equal the eccentricities DF and DR. Depending on ship type, however, the spatial conditions often require a different arrangement and movement of actuators 11 and 12, for instance in the direction of the axes X and Y in FIG. 1. To control the actuators it is thus necessary to convert the eccentricities DF and DR through a rotation of the coordinate system to control variables Dx and Dy for the adjustment paths DX and DY.
For this purpose, the transformer device 13 is employed which provides the control inputs of actuators 11 and 12. The input signals of transformer device 13 are provided by an arithmetic unit 14 and are derived from the control inputs F and R.
The control input F for the travel pitch is determined by a travel command which may be adjusted by means of a speed control lever 15 and an associated transmitter 16, while the control input R for the rudder pitch is determined by a rudder command which is adjusted by means of a rudder wheel 17 and an associated transmitter 18.
According to the aforementioned German Pat. No. 2 029 995, the mechanical forces for adjustment of the control axes are applied by servomotors which are coupled together with one another since they are jointly attached to the control point A.
It is, therefore, desired to provide a control for a propeller wheel which maintains exact control of a ship. It is further desired to provide such a control which is adapted easily to various servomotors, drive motors, ship types and propeller designs, and which requires for such adaptation only the setting of suitable electrical parameters in the electronic control system. It is still further desired to provide a simple electrical and practically maintenance-free control which achieves the same measure of safety and ruggedness as conventional, strictly mechanical controls.